The present invention relates to machines, and, in particular, relates to micromachines, and further, relates to free-standing microtube devices.
In recent years there has been tremendous interest in miniaturization due to the high payoff involved. One area of current interest is microelectromechanical systems (MEMS) and the closely related fields of micro-fluidics and micro-optical systems. Presently, these technologies involve micro-machining on a silicon chip to produce numerous types of devices, such as sensors, detectors, gears, engines, actuators, valves, pumps, motors, and mirrors on the micron scale. The first commercial product to arise from MEMS was the accelerometer manufactured as a sensor for air-bag actuation. On the market today, there are also micro-fluidic devices, mechanical resonators, biosensors for glucose, and disposable blood pressure sensors that are inserted into the body.
The vast majority of microsystems are made almost exclusively on planar surfaces using technology developed to fabricate integrated circuits. That is, the fabrication of these devices takes place on a wafer and the device is formed layer-by-layer with standard clean-room techniques that include e-beam or photolithography, thin-film deposition, and wet or dry etching.
Although there have been numerous and very innovative successes using these silicon wafer-based technologies, there are some disadvantages. Since it requires the building-up of many layers of different materials as well as surface and bulk micro-machining there are some very difficult material science problems to solve. These include differential etching and laying down one material without damaging a previous layer. In addition, there are the problems associated with interconnecting layers in a chip with different functions. An example of this would be a micro-fluidic device in which there are both fluidic and electronic functions. Clearly, there are numerous materials' issues central to this technology.
In addition to these processing problems, there are other limitations inherently associated with conventional lithographic techniques that are based on planar silicon. For example, in some applications such as those that involve surface tension in fluidics, it is important to have a circular cross-section. However, it is impossible to make a perfectly round tube or channel on a chip with current technology. Instead channels are made by etching a trench and then covering the trench with a plate. This process can only produce angled channels such as those with a square, rectangular, or triangular cross-section.
Thus, there exists a need for microtube devices not associated with planar technology.